1 files changed, 100 insertions, 0 deletions
diff --git a/absl/crc/crc32c.cc b/absl/crc/crc32c.cc
new file mode 100644
index 00000000..82865df5
--- /dev/null
+++ b/absl/crc/crc32c.cc
@@ -0,0 +1,100 @@
+// Copyright 2022 The Abseil Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include "absl/crc/crc32c.h"
+
+#include <cstdint>
+
+#include "absl/crc/internal/crc.h"
+#include "absl/crc/internal/crc32c.h"
+#include "absl/crc/internal/crc_memcpy.h"
+#include "absl/strings/string_view.h"
+
+namespace absl {
+ABSL_NAMESPACE_BEGIN
+
+namespace {
+
+const crc_internal::CRC* CrcEngine() {
+  static const crc_internal::CRC* engine = crc_internal::CRC::Crc32c();
+  return engine;
+}
+
+constexpr uint32_t kCRC32Xor = 0xffffffffU;
+
+}  // namespace
+
+namespace crc_internal {
+
+crc32c_t UnextendCrc32cByZeroes(crc32c_t initial_crc, size_t length) {
+  uint32_t crc = static_cast<uint32_t>(initial_crc) ^ kCRC32Xor;
+  CrcEngine()->UnextendByZeroes(&crc, length);
+  return static_cast<crc32c_t>(crc ^ kCRC32Xor);
+}
+
+// Called by `absl::ExtendCrc32c()` on strings with size > 64 or when hardware
+// CRC32C support is missing.
+crc32c_t ExtendCrc32cInternal(crc32c_t initial_crc,
+                              absl::string_view buf_to_add) {
+  uint32_t crc = static_cast<uint32_t>(initial_crc) ^ kCRC32Xor;
+  CrcEngine()->Extend(&crc, buf_to_add.data(), buf_to_add.size());
+  return static_cast<crc32c_t>(crc ^ kCRC32Xor);
+}
+
+}  // namespace crc_internal
+
+crc32c_t ComputeCrc32c(absl::string_view buf) {
+  return ExtendCrc32c(ToCrc32c(0), buf);
+}
+
+crc32c_t ExtendCrc32cByZeroes(crc32c_t initial_crc, size_t length) {
+  uint32_t crc = static_cast<uint32_t>(initial_crc) ^ kCRC32Xor;
+  CrcEngine()->ExtendByZeroes(&crc, length);
+  return static_cast<crc32c_t>(crc ^ kCRC32Xor);
+}
+
+crc32c_t ConcatCrc32c(crc32c_t lhs_crc, crc32c_t rhs_crc, size_t rhs_len) {
+  uint32_t result = static_cast<uint32_t>(lhs_crc);
+  CrcEngine()->ExtendByZeroes(&result, rhs_len);
+  return static_cast<crc32c_t>(result) ^ rhs_crc;
+}
+
+crc32c_t RemoveCrc32cPrefix(crc32c_t crc_a, crc32c_t crc_ab, size_t length_b) {
+  return ConcatCrc32c(crc_a, crc_ab, length_b);
+}
+
+crc32c_t MemcpyCrc32c(void* dest, const void* src, size_t count,
+                      crc32c_t initial_crc) {
+  return static_cast<crc32c_t>(
+      crc_internal::Crc32CAndCopy(dest, src, count, initial_crc, false));
+}
+
+// Remove a Suffix of given size from a buffer
+//
+// Given a CRC32C of an existing buffer, `full_string_crc`; the CRC32C of a
+// suffix of that buffer to remove, `suffix_crc`; and suffix buffer's length,
+// `suffix_len` return the CRC32C of the buffer with suffix removed
+//
+// This operation has a runtime cost of O(log(`suffix_len`))
+crc32c_t RemoveCrc32cSuffix(crc32c_t full_string_crc, crc32c_t suffix_crc,
+                            size_t suffix_len) {
+  crc32c_t crc_with_suffix_zeroed =
+      suffix_crc ^ full_string_crc ^
+      ExtendCrc32cByZeroes(ToCrc32c(0), suffix_len);
+  return crc_internal::UnextendCrc32cByZeroes(
+    crc_with_suffix_zeroed, suffix_len);
+}
+
+ABSL_NAMESPACE_END
+}  // namespace absl